Russian leader Putin unleashed a full-scale invasion on Thursday that has killed dozens of people, forced more than 50,000 to flee Ukraine in just 48 hours and sparked fears of a new Cold War in Europe.

After Ukrainian forces fought Russian troops advancing on the capital Friday, not long after midnight, Zelensky warned the nation to stay on its guard.

"This night will be more difficult than the day. Many cities of our state are under attack," he said in a video address.

"Special attention on Kyiv –- we cannot lose the capital," he added.

"I am turning to our defenders, male and female, on all fronts: this night the enemy will use all the forces it has to crush our defence in a treacherous, harsh and inhumane way," he said. 

"Tonight they will attempt a storming" of the capital, he added in an apparent reference to Kyiv. 

Zelensky, who had earlier called for a stronger response from the West, said he spoke to leaders including French President Emmanuel Macron, German Chancellor Olaf Scholz and US President Joe Biden.

"We have agreed on more aid, more support, significant support for our state," he said.

The United States, Canada, Britain and the European Union announced further sanctions against Russia on Friday, including against Putin himself and his Foreign Minister Sergei Lavrov.

Russia said the sanctions against the pair were "a demonstration of the complete impotence of the foreign policy" of the West.

Ukrainian soldiers were seen in Kyiv Friday as Russian troops advanced

"We have reached the line after which the point of no return begins," Russian foreign ministry spokeswoman Maria Zakharova said.

Moscow also vetoed -- as expected -- a UN Security Council resolution that deplored "in the strongest terms" Russia's invasion, while China, Indian and the United Arab Emirates abstained.

Putin had earlier described the Ukrainian government as "terrorists" and "a gang of drug addicts and neo-Nazis".

"Take power in your own hands," he told the Ukrainian military in a televised address, urging it to topple Zelensky.

The Ukrainian leader responded early Friday by posting a self-shot video on social media of himself on a Kyiv street, vowing to stay and defend the capital.

"We're all here. Our military is here. Citizens in society are here. We're all here defending our independence, our country, and it will stay this way," Zelensky said.

The US-led military alliance NATO said the Ukrainians were putting up a stiff resistance to the Russian threat.

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